In automotive alternators using a Lundell rotor mounted with fans, cooling airflows are generated centrifugally by the fans together with rotation of the rotor to cool stator coil ends, brackets transmitting stator heat, etc. A rectifier and a regulator are also cooled by cooling airflows sucked in by the fans. Since these cooled bodies each have a heat resistance limit, if cooling is not achieved sufficiently, for example, the heat resistance limit may be exceeded, causing damage, and if that is to be prevented, it may be necessary to reduce flowing electric current values. In other words, electric current generated in the alternator must be suppressed, reducing output performance.
In environments surrounding automotive alternators, there has been a tendency in recent years for thermal environments to be high in temperature and severe due to factors such as rising ambient temperatures in engine compartments, increases in onboard electrical equipment, etc., accompanying reductions in engine compartment size, and high-density arrangement of peripheral parts in engine compartments, etc.
In addition, in order to meet demands for compact size, light weight, and high output that are sought in automotive alternators, automotive alternators show a tendency toward size reduction, which leads to reductions in cooling fan diameters, but there is a possibility that this may be accompanied by deterioration in automotive alternator cooling due to reductions in cooling airflow rate, and there is an urgent need to achieve improvements in automotive dynamoelectric cooling to overcome these problems.
In answer to demands of this kind, alternators are known in which cooling efficiency is improved by combining a front-end cooling fan having oblique-flow blades and a rear-end cooling fan having centrifugal blades, fixing the rear-end cooling fan to an end surface of a Lundell pole core away from a pulley, fixing the front-end cooling fan to an end surface of the pole core near the pulley, and selecting oblique-flow blades having an optimal shape (See Patent Literature 1, for example).
Patent Literature 1
Japanese Patent Laid-Open No. HEI 09-154256 (Gazette)
However, In an automotive alternator of the above configuration, settings are required that place importance on better cooling in response to increases in the amount of heat generated by electrical components such as three-phase stator coils, rotor coils, etc., in order to adapt to compact size and high output, but cooling airflow rate cannot be made to catch up merely by optimizing the shape of the oblique-flow blades of the front-end cooling fan, and means for increasing the airflow rate must inevitably be considered.
Conceivable examples of means for improving the cooling airflow rate include increasing the number of oblique-flow blades in the cooling fan, and increasing the area of the oblique-flow blades, etc., but in manufacturing methods involving press-forming ferrous metal plates, etc., since a plurality of oblique-flow blades are cut and raise from a single sheet of generally disk-shaped base material, increasing the number of blades and increasing the area of the blades conflict with each other, and one problem has been that normally the number of blades and the area of the blades must be selected by making a certain trade off, making it extremely difficult to achieve both improvements in output and reductions in size in automotive alternators.